Hi Jono,
Please let me know if I have this right:
1. You have a script called /conditions.php which works fine if you remove the header("Location:...") code which you recently tried adding.
2. You want this script to appear to serve requests that look like /conditions-123.html instead of /conditions.php?123
3. There aren't actually any /conditions-123.html files, you just want to make it appear like they exist.
If that's correct, you'll only need the rewrite rule, not the header("Location:...") code. Your rewrite code looks good, (I tried it myself here and it worked fine,) so if things still aren't working, you could try a simpler rewrite to make sure rewrites are working (e.g. rewrite foo.html to bar.html) or if you have access to httpd.conf [url http://www.latenightpc.com/blog/archives/2007/09/05/a-couple-ways-to-debug-mod_rewrite]you could try turning on rewrite logging[/url] so see if anything is going awry.
I'm afraid there isn't too much else we can do here on the forums, but our consulting team could probably get this figured out for you if all else fails. Please let me know if you're interested in that.
I hope this helps. Please let us know how it goes or if you have any questions.
All the best,
Chris